1. Technical Field
The present invention generally relates to methods of analyzing tread patterns for tire noise. More particularly, the invention relates to a method for comparing tread pattern tire noise created by variations in lug stiffness. The invention specifically relates to a method for analyzing tire noise created from variations in tread lug stiffness based on the distribution of the lugs in the tire noise pitch sequence.
2. Background Information
One aspect of tire design involves minimizing undesirable tire noise. Tire noise is generated when the lugs of the tread pattern contact the road surface. An unvarying tread pattern creates an undesirable mono pitch sound. Tire designers vary the tread pattern to avoid mono pitch sounds. The tread patterns are typically varied by altering the size of the tread pitches around the circumference of the tire. Varying the sizes of the tread pitches tends to reduce mono pitch tire noise by broadening the frequency domain of the noise spectrum but undesirable noise in the time domain can still be created.
Tread patterns are currently analyzed by comparing the tire noise generated by different variations in the tread pitches. Known analysis techniques allow the tire designer to select a pitch pattern for the tread design that generates acceptable tire noise. One such technique uses the Fourier spectrum of the pitch sequence to identify objectionable pitch sequences. Another technique disclosed in U.S. Pat. No. 6,112,167 analyzes portions of the pitch sequence around the circumference of the tire. Although these techniques have been effective, tire designers have found that known techniques can result in tire noise pitch sequence designs that pass initial screening while still having undesirable tire noise. Tire molds having such sequences must be rebuilt or modified to reduce the undesirable noise. One cause of undesirable noise is tire noise attributed to the variations in the lug stiffness around the circumference of the tire.
When the size of the tread pitches is varied, the size of the lugs of the tread pattern is varied. The lugs thus have different stiffnesses and produce different sound amplitudes when they contact the road surface. These differences create sound amplitude variation that can make an otherwise desirable pitch sequence undesirable. In the past, this undesirable tire noise was not analyzed and tires would be produced before the undesirable noise was recognized. If the customer objected to the noise, the tire manufacturer would have to scrap the expensive tire mold or would have to modify the mold. The art thus desires a secondary screening method that allows the tire designer to compare a group of otherwise desirable pitch sequences. Such a secondary screening method would analyze the tire noise generated from lug stiffness variations.